At your age, the best way to have healthy bones is to eat a balanced diet having calcium such as milk, curd and other dairy products, ragi/nachni, spinach, broccoli, bhindi/okra, kismis, etc. and seafish & egg whites. You also need to get adequate Vitamin D, got from exposure to sunlight for half an hour at least thrice a week. You need to perform regular exercise, esp. weight bearing, to increase bone density. If you have stiffness in the morning, or pain & swelling in multiple joints, you may need to get some blood tests done.